Aside from the smartphone purchase data, Nielsen shared additional information on the platforms and handset makers that are winning and losing the battle for consumer awareness:

Among all smartphone owners, the Android and iOS platforms lead the way with 51.8 percent and 34.3 percent of sales respectively. BlackBerry devices account for 8.1 percent while all other platforms make up the remaining 5.9 percent of ownership.

A standout data point — broken out from all smartphone owners — is the sales share of those purchasing a smartphone in the most recent three months. There’s little change at the top: Android is good for 54.6 percent of sales while iOS also makes a gain: Up to 36.3 percent of recent sales. But some of those gains come at the expense of BlackBerry devices, which only account for 4.0 percent. This drop in sales to recent phone buyers, compared to smartphone owners as a whole, underscores Research In Motion’s problems. Regardless of how good BlackBerry 10 may or may not be when it arrives early next year, it may be too late in the minds of buyers.

Being the only handset maker to use its own platform, save BlackBerry, Apple holds the lead among manufacturers. Samsung is a distant second with 17 percent of all Android device sales, while HTC has 14 percent; closer than I’d expect, although HTC’s One series launched before Samsung’s Galaxy S III in the U.S.

To date, Windows Phone devices are still being outsold by all other platforms, including Microsoft’s old Windows Mobile platform. The newer phones accounted for 1.7 percent of device sales in the second quarter of this year while Windows Mobile devices were 3 percent of the total smartphone market in the U.S.

There’s little data to suggest that what’s been happening in smartphone sales won’t continue to happen. Android and iOS hold momentum that RIM hasn’t had in some time and that Microsoft is still trying to find with its solid mobile platform revamp. We keep looking for the third horse this race, but at this point, there’s only a pair of ponies running at full speed.